1. Field of the Invention
The invention relates to a family of passive attenuators for shelter protection against explosions. Attenuators are devices which allow ventilation air to pass through and are capable of reducing intensity of pressure and impulse of impinging blast waves from the outside.
2. Description of a Related Art
A wide variety of attenuation devices are available and may be classified broadly on the basis of their mode of operation, as passive or active. Active attenuators (or blast valves) have moving parts activated by the blast pressure which can close ventilation gaps shutting out the blast. These closure times are typically of the order of 5 ms. For conventional weapons, this response time is too slow for effective attenuation. In addition, it has been reported that some types of active valves were found to be relatively fragile, seizing shut under repeated high blast pressures from conventional weapons. The valves also have to undergo frequent maintenance to ensure free movement and proper seating of moving pans.
Passive attenuators have no moving pans and reduce the pressure and impulse by combined effects of reflection, expansion, contraction and deviation contributed by the geometry of the attenuator. They are rugged and require little maintenance.